[Illustration: Sensitive Fern. Gradations from Leaf to Fruit. _Obtusilobata_ Form]
Fronds one to three feet high, scattered along a creeping rootstock, broadly triangular, deeply pinnatifid, with segments sinuately lobed or nearly entire. Veins reticulated with fine meshes. The fertile fronds shorter, closely bipinnate with the pinnules rolled up into berry-like structures which contain the spore cases. (The name in Greek means a closed vessel, in allusion to the berry-like fertile segments.) The sensitive fern is so called from its being very sensitive to frost. The sterile and fertile fronds are totally unlike, the latter not coming out of the ground until about July, when they appear like rows of small, green grapes or berries, but soon turn dark and remain erect all winter, and often do not discharge their spores until the following spring. The little berry-like structures of the fertile frond represent pinnules, bearing fruit-dots, around which they are closely rolled. As Waters remarks, "Most ferns hold the sori in the open hand, but the sensitive fern grasps them tightly in the clenched fist."
Var. _obtusilobatà_ is an abortive form with the fertile segments only partially developed. The illustration shows several intermediate forms.
[Illustration: Sensitive Fern. _Onoclea sensibilis_]
[Illustration: Sensitive Fern, Fertile and Sterile Fronds on one Stock _Onoclea sensibilis_ (From the collection of Mr. and Mrs. L.P. Breckenridge)]
[Illustration: Ostrich Fern. _Onoclea Struthiopteris_. Fertile Fronds]
_Onoclea struthiópteris_. PTERETIS NODULOSA
_Struthiópteris Germánica_. _Matteùccia struthiópteris_
Fronds two to eight feet high, growing in a crown; broadly lanceolate, pinnate, the numerous pinnæ deeply pinnatifid, narrowed toward the channeled stipe. Fertile fronds shorter, pinnate with margins of the pinnæ revolute into a necklace form containing the sori.
[Illustration: Ostrich Fern. Sterile Fronds (New Hampshire)]
The rootstocks send out slender, underground stolons which bear fronds the next year. Sterile fronds appear throughout the summer, fertile ones in July. Seen from a distance its graceful leaf-crowns resemble those of the cinnamon fern. An intermediate form between the fertile and sterile fronds is sometimes found, as in the sensitive fern. This handsome species thrives under cultivation. For grace and dignity it is unrivaled, and for aggressiveness it is, perhaps, equaled only by the lady fern. For the climax of beauty it should be combined with the maidenhair. The ostrich fern is fairly common in alluvial soil over the United States and Canada.